| Since the reform and opening up.China’s urbanization rate has increased from 17.92%in 1978 to 56.1%in 2015.It would continue to grow at a rate of one percentage point a year.China’s urbanization rate is expected to exceed 60%by 2020.Because of urbanization,the transformation of rural population into urban residents has brought tremendous social welfare to China.A large number of people gather in the city to promote the drastic expansion of urban built-up areas.As we known,the development of cities is influenced by both human activities and natural factors,while the expansion of cities also affects people’s activities and natural environment.With the development of remote sensing and geographic information technology,the monitoring and research technology for urban expansion is constantly innovating.The appearance of night light data promotes the development of urban expansion monitoring with large scale and long time series in particular.The study extracts urban built-up areas in China from night lighting data in 1992,1997,2002,2007,2012 and 2017.Two kinds of night light data are pretreated by different methods to improve the quality of extraction results.DMSP/OLS data are processed by mutual correction and continuity correction,while NPP/VIIRS data are synthesized by monthly data and logarithmic transformation is performed.The segmentation thresholds of urban built-up areas of each provincial administrative unit are calculated based on the boundary information of urban built-up areas,which can reduce the impact of different thresholds caused by unbalanced regional development and further improve the extraction accuracy of built-up areas.According to threshold segmentation,urban built-up areas in China are extracted and their accuracy is verified.Based on the extracted results,the urban expansion speed and urban expansion intensity were used to analyze the characteristics of urban area change in China from 1992 to 2017.In order to further explore the expansion law of urban built-up areas in the process of rapid development in China,the three urban agglomerations,Beijing-Tianjin-Hebei,Yangtze River Delta and Pearl River Delta are typical areas of rapid development in China,are selected to analyze the spatial and temporal changes of urban expansion.Finally,simulation of China’s Urban Expansion in the Future Based on ANN-Markov-CA Composite Model.The main conclusions are as follows:(1)The interpretation accuracy reaches 81.68%,which indicates that Canny edge detection algorithm can effectively improve the accuracy of building area extraction based on night light data.Pre-processing measures are adopted for night lighting data,which enhances the expressive ability of urban built-up area information in night lighting data and improves the quality of urban built-up area extraction results.According to Canny edge detection method,the boundary information of urban built-up area can be effectively detected.The threshold values of urban built-up areas are calculated according to the boundary information partition,which reduces the errors caused by different levels of regional economic development in the extraction of urban built-up areas.In order to verify the accuracy of the extraction results,the overlap area is 80.06%by superimposing the extracted results with the built-up area extracted from Landsat8 data.The Canny edge detection algorithm is feasible for night lighting extraction of urban built-up areas.In terms of urban expansion intensity,the urban expansion intensity in the region of East of Hu Huanyong Line is higher than that in the area west of Hu Huanyong Line and China as a whole.Compared with the region of West of Hu Huanyong Line,the urban expansion intensity in the region of East of Hu Huanyong Line is 3.5 times as low as that in the region of West of Hu Huanyong Line,and the maximum is more than 8 times.(2)The area of built-up urban areas in China increased by 5.7 times between 1992and 2017.The region of East of Hu Huanyong Line contributes most to China’s urban expansion.From 1992 to 2017,the area of urban built-up areas in China increased steadily,with the newly added area of urban built-up areas exceeding 10,000 km~2 in each period.In2017,the area of urban built-up areas was 5.7 times that of 1992.The area of East of Hu Huanyong Line has absolute advantages in area change,urban expansion speed and urban expansion intensity.In terms of area change,the gap between the two sides gradually increased from 16119 km~2 in 1992 to 77792 km~2 in 2017.In terms of urban expansion speed,the smallest gap between the two sides is 1427 km~2,which is larger than the maximum of 823.6 km~2 in the region of West of Hu Huanyong Line.Therefore,the region of East of Hu Huanyong Line contributes most to China’s urban expansion.(3)The spatial distribution of urban expansion in China is closely related to natural environment and economic development.From 1992 to 2017,the Yangtze River Delta,the Pearl River Delta and Beijing,Tianjin and Hebei have been the most prominent areas of urban expansion in China.With the passage of time,the prominent areas of urban expansion have shifted to the west.In the center of regional development,such as provincial capital cities and municipalities directly under the Central Government,urban expansion is significant.At the same time,natural conditions restrict the spatial distribution of urban expansion.Urban expansion is significant in the overlapping areas of Eastern monsoon climate and flat terrain.Urban expansion is less distributed in cold and arid regions.Therefore,the natural environment conditions and socio-economic development affect the spatial distribution of urban expansion in China.(4)The urban expansion of the three metropolitan agglomerations mainly concentrates on the periphery of the central cities in the urban agglomeration,and the transfer of the urban center of gravity is related to the spatial and temporal changes of urban built-up area expansion.From 1992 to 2017,the built-up area of the three metropolitan agglomerations gradually increased,with an average growth rate of 43.72%in Beijing,Tianjin and Hebei,56.14%in the Yangtze River Delta and 34.60%in the Pearl River Delta.The Yangtze River Delta has the largest urban built-up area.In the spatial distribution of urban expansion,the most prominent areas are mainly concentrated in the central cities within the urban agglomeration.The mountainous areas and mountains in the region affect the spatial distribution of urban built-up areas and urban expansion.Urban expansion distribution is affected by social and economic conditions and natural conditions.The change of the center of gravity of the three metropolitan agglomerations is influenced by the spatial distribution of urban expansion.(5)The accuracy of ANN model in evaluating the suitability of urban expansion is0.864,which is higher.The ANN model is suitable for evaluating the suitability of urban expansion.The simulation results show that the hot areas of urban construction and expansion in China have shifted,but the limitations of Hu Huanyong Line are still difficult to break through.The accuracy of K-fold validation method in evaluating the training results of ANN model is 0.864.The CA-Markov model is used to simulate urban expansion in China.The Kappa coefficient is 0.78.Therefore,the ANN-Markov-CA composite model has high simulation accuracy and is suitable for urban expansion simulation research.According to the simulation results,it is found that the hot areas of urban expansion have shifted.Although the scale of urban expansion in Beijing-Tianjin-Hebei,Yangtze River Delta and Pearl River Delta is still considerable,it is more prominent in Chengdu-Chongqing urban agglomeration,Guanzhong Plain urban agglomeration,Central Plains urban agglomeration and the middle reaches of Yangtze River.According to the existing natural and social economic conditions,it is difficult for China’s urban expansion to break through the restrictions of Hu Huanyong Line. |
PDF Full Text Request